Resins with excellent transparency are used in applications such as optical materials, lighting materials, signboards, decorative members and the like. In these applications, the resins are sometimes required to be flame resistance.
As a method for increasing flame resistance of a resin, addition of an inorganic compound such as basic magnesium carbonate to the resin to obtain a resin composition is known (see Patent Document 1, for example). However, this resin composition usually has low transparency and is therefore unsuitable for applications where excellent transparency is required, such as for optical materials and the like.
As another method for increasing the flame resistance, addition of a phosphoric acid ester or a halogen-containing condensed phosphoric acid ester to obtain a resin composition is known (see Patent Documents 2, 3, and 4, for example). However, the phosphoric acid ester or the halogen-containing condensed phosphoric acid ester may bleed out to the surface of this resin composition over time, leading to surface whitening and low flame resistance. Upon burning, a resin composition comprising a halogen-containing condensed phosphoric acid ester, in particular, may generate halogen gas, which is toxic and causes metal corrosion.
Also suggested is a copolymer of a phosphonate monomer or a phosphate monomer with a (meth)acrylic acid alkyl ester (see Patent Documents 5 and 6 and Non-patent Documents 1 and 2). In order to increase flame resistance of this copolymer, however, the proportion of the phosphonate monomer or the phosphate monomer that undergoes copolymerization needs to be high, resulting in a low glass transition temperature of the resulting copolymer. Therefore, this copolymer is unsuitable for applications under high temperatures.